1. Field of the Invention
The present invention relates to an image forming apparatus such as an electronic copy machine having an auto density control mode and a manual density control mode.
2. Description of the Related Art
In general, an electronic copy machine comprises an auto density control mode, which automatically adjusts density control of a image lamp in accordance with density of an original document, and a manual density control mode which can arbitrarily change density of a image regardless of density of the original document.
Conventionally, as described in Japanese Patent Disclosure (Kokai) No. 2-39168, in the copy machine, which in the manual density control mode changing development bias voltage uses a slide volume, data at the position of the slide volume is read and development bias voltage is adjusted based on this data. In this machine, in order to manually set the density, a slide volume on the operation panel is moved to a suitable density position, and the mode of this machine is changed to manual mode.
However, in a machine having an automatic mode changing function, when the operator touches the slide volume by mistake, the mode is erroneously changed to a manual mode opposite to the operator's intention. Therefore, it is a problem that if the operator carries out copying by changing to the manual mode, the copier would probably miss a copy.